若a\b=c\d=e\f=3\4求a+2c+3e\b+2d+3f

根据题意
令a=3m,b=4m,c=3n,d=4n,e=3k,f=4k
那么(a+2c+3e)/(b+2d+3f)=(3m+6n+9k)/(4m+8n+12k)=3(m+2n+3k)/4(m+2n+3k)=3/4
或者利用比的性质
a/b=cd=ef=34
那么
a/b=2c2d=3e3f=34
(a+2c+3e)(b+2d+3f)=3/4